1. Field of the Invention
The present invention relates to an eye refractive power measurement apparatus for measuring eye refractive power of an eye of an examinee objectively.
2. Description of Related Art
Conventionally, there is known an eye refractive power measurement apparatus which projects spot-shaped measurement light onto a fundus via a central pupillary portion and photo-receives the measurement light reflected from the fundus via a peripheral pupillary portion using a two-dimensional photodetector or the like to obtain eye refractive power based on a photo-receiving result thereof. In such an apparatus, in order to ensure measurement accuracy, the measurement light reflected from the fundus is arranged to be photo-received via a ring-shaped region of 2 mm in inside diameter and 3 mm in outside diameter on a pupillary surface.
However, if a pupil diameter is smaller than the ring-shaped region, sometimes measurement cannot be performed. Therefore, to cope with this problem, there is proposed an apparatus which rotates a measurement part including a measurement optical system so as to revolve about a pupil center (see Japanese Patent Application Unexamined Publication No. 2002-17676).
However, the apparatus which rotates the entire measurement part including the measurement optical system involves extensive driving and is inappropriate for high-speed rotation. In addition, as a fixation target presenting optical system for presenting a fixation target to an eye is included in the measurement part, if the measurement part is rotated, the presented fixation target is also unintentionally rotated; therefore, measurement cannot be performed in a stable fixation state. Thus, this kind of apparatus is not in the actual use.
Further, to deal with an eye with a small pupil diameter, it is conceivable that the ring-shaped region on the pupillary surface is made even smaller. In this case, however, corneal reflection or crystalline lens reflection of the projected measurement light tends to become noise, and for an ordinary eye with a large enough pupil diameter (a normal eye), measurement accuracy is sometimes contrarily lowered.